Tools and methods for constructing large diameter underground piles

Abstract

Methods are provided for the creation of large diameter piles in all types of soils (cohesive, cohesionless or rocky), particularly for the construction of bulkheads made of juxtaposed or secant piles, while maintaining the deviation from the vertical well below the limit ≦2% required by European standard EN 1536. The invention reduces verticality errors, advantageously exploiting the accuracy provided by the directional drilling technology. Tools for implementing such methods are also provided.

The invention claimed is: 
     
       1. A method of constructing large diameter underground piles, comprising the steps of:
 a) providing an underground, small diameter cylindrical pilot core made of mechanically erodible material extending along a central axis of a pile to be constructed; 
 b) excavating the soil around the pilot core using the pilot core as a guide for a drilling tool, the tool comprising: 
 a central, cylindrical guiding cavity adapted to fit around the core; 
 first lower cutter elements for drilling the soil underneath the tool; and 
 second inner cutter elements located above the cylindrical guiding cavity, for milling the top of the core as the tool moves downward guided along the same core; and 
 c) milling the top of the core as the tool moves downward guided along the core and filling the borehole formed by the soil excavation with concrete. 
 
     
     
       2. The method of  claim 1 , wherein said step a) comprises the steps of:
 excavating a small diameter pilot borehole in the ground; and 
 inserting a cylindrical pilot tube of a mechanically erodible material into the pilot borehole to form the core. 
 
     
     
       3. The method of  claim 2 , further comprising filling the pilot tube with a hardening mixture. 
     
     
       4. The method of  claim 3 , wherein the step of inserting the pilot tube is preceded by a step of driving a casing into the pilot borehole, and wherein the pilot tube is inserted into said casing. 
     
     
       5. The method of  claim 4 , wherein the step of filling the pilot tube with the hardening mixture is followed by a step of removing the casing from the pilot borehole. 
     
     
       6. The method of  claim 3 , wherein the hardening mixture which is cast in the pilot tube comprises a fiber reinforced cement mixture. 
     
     
       7. The method of  claim 2 , wherein the pilot borehole is drilled using steerable drilling techniques. 
     
     
       8. The method of  claim 1 , wherein step a) further comprises:
 prefabricating the cylindrical pilot core, and 
 driving the prefabricated pilot core into the ground along the central axis of the pile to be constructed. 
 
     
     
       9. The method of  claim 8 , wherein said driving step is preceded by a step of preliminarily drilling a small diameter pilot borehole in the ground, and that subsequently, during said driving step, the prefabricated pilot core is driven into the pilot borehole. 
     
     
       10. The method of  claim 8 , wherein the prefabricated pilot core is driven directly into the ground without drilling a preliminary pilot borehole. 
     
     
       11. The method of  claim 8 , wherein the step of prefabricating the pilot core comprises:
 providing a cylindrical pilot tube of mechanically erodible material, and 
 filling the pilot tube with a hardening mixture. 
 
     
     
       12. The method of  claim 8 , wherein the prefabricated pilot core comprises a full cylindrical body made of a single piece. 
     
     
       13. The method of  claim 1 , wherein the step of excavating the soil around the pilot core is performed using a reverse circulation drilling technique, which comprises:
 flooding a widened borehole excavated by the tool with a fluid, and 
 sending compressed air to the tool through a first conduit in a drill string rod having a second conduit through which the fluid is sent to a surface with cuttings made by the drilling tool. 
 
     
     
       14. A bucket type drilling tool comprising
 a first lower cutter element for drilling the soil underneath the tool; 
 a central cylindrical guiding cavity extending upward from an open bottom base under which the first lower cutter element is fixed; 
 a second inner cutter element arranged above the cylindrical guiding cavity for milling the top of a pilot core as the tool moves downward guided along the pilot core; 
 a roof with an upper connection providing mechanical connection to a drill string; 
 a substantially cylindrical side wall connecting the bottom base to the roof; 
 a tubular inner portion, arranged at least partially above the bottom base, the tubular inner portion extending coaxially within the side wall and forming the central cylindrical guiding cavity; 
 articulation units pivotally connecting the bottom base to the side wall; and 
 releasable locking units for locking the bottom base to the side wall in an excavating arrangement, and for releasing the bottom base from the side wall so as to allow the bottom base to tilt around the articulation units and open to empty the bucket type drilling tool. 
 
     
     
       15. The drilling tool of  claim 14 , wherein the second inner cutter elements are arranged spaced above the cylindrical guiding cavity and wherein the cylindrical guiding cavity is open at the top. 
     
     
       16. The drilling tool of  claim 14 , wherein the cylindrical guiding cavity provides a plurality of side openings through which cuttings of the pilot core after being eroded are allowed to fall out onto the bottom base of the tool.